A comparative study of stock assessment and stock management between the Pacific stock of chub mackerel Scomber japonicas and the Northeast Atlantic mackerel Scomber scombrus

摘要

Catches of the Pacific stock of chub mackerel Scomber japonicus have been dominated by fishes of ages 0 to 2. On the other hand, catches of the Northeast Atlantic mackerel Scomber scombrus have mainly consisted of fishes aged 3 or over. In order to study the causes of the difference, we compared biological traits, stock dynamics, stock assessments, stock management and fisheries management. Natural mortality coefficient of the Pacific stock of chub mackerel (0.4/year) was higher than that of the Northeast Atlantic mackerel (0.15/year). Also, weight at age of the Pacific stock of chub mackerel was larger than that of the Northeast Atlantic mackerel. Yield per recruitment analyses indicated that the desirable age at first capture for the Pacific stock of chub mackerel was two or three years younger than that for the Northeast Atlantic mackerel. Therefore, we concluded that one of the causes of the difference of catch at age was differences of biological traits; the effects of other factors were unclear. We also point out the potential problem of recent stock management of the Northeast Atlantic mackerel.